A conventional supporting and driving mechanism of a rotatable body is explained with reference to the photoconductive drum of an electrophotographic printing machine (i.e., a plain paper copyer, a laser beam printer, etc.). The drum should be supported at a fixed position and should be rotated in the position stably in an operation. For supporting the drum, the axis of the drum is received by a U-shaped recess of the machine frame. For driving the drum, a gear (driven gear) provided at an end of the drum is engaged with another gear (driving gear) of a driving unit fixed to the machine frame.
A problem of the conventional supporting and driving mechanism is that the support of the drum is unstable when the driving force applied from the driving gear to the driven gear is directed upward even though slightly, i.e., when the driving force has any upward component force, because the drum tends to lift toward the opening of the U-shaped recess. The lift also loosens the engagement of the driving and driven gears which leads to an unstable rotation of the drum. Normally the inner wall of the recess is made of copper-based sintered alloy for the purpose of less friction, less abrasion and more electric conductivity between the drum and the ground, but the long time surface slip between the static recess and the rotating axis causes abrasion both on the recess surface and the axis surface, and the rotation will become hard and unstable.